1. Field of the Invention
The present invention relates generally to mobile computers and, more particularly, to a method for automatically computing the local time and date of a mobile computer, when a user has traveled to a time zone different from his or her home time zone.
2. Description of the Prior Art
With the advent of mobile computers, users are now capable of taking their computer systems with them as they travel. However, as user's travel with their systems through different time zones, the time and date stored within the computer system does not adjust. Thus, as the mobile computer travels through various time zones, the system stays set to the date and time zone of its home base.
Normally, the user ignores the time difference rather than going through the trouble of manually updating the internal clock, especially where only one computer is involved and the user is not traveling for an extended period of time out of his or her home time zone. However, when two separate users, in different time zones, are attempting to synchronize work, the importance of having their respective computer systems represent the correct time becomes apparent.
Thus, what is needed in the art is a method for computing, storing and/or displaying the local time and date on a mobile computer, when a user has traveled with the computer to a time zone different from his or her home time zone. It is therefore, to the effective resolution of the aforementioned problems and shortcomings that the present invention is directed.
The present invention utilizes cellular telephone technology to achieve the objects of the present invention. The public telecommunication systems can be divided generally into two components: the public switched telephone network (wireline) and the cellular network. The cellular or mobile subscriber network consists of numerous mobile telephone subscribers who remain in communication with one another and with telephones connected to the public switched telephone network by virtue of radio links within a plurality of adjacent cells. Each cell is illuminated by the radio transmissions from a particular base station which covers that cell and which is in turn coupled to a mobile switching center ("MSC")which controls the radio linkages between many different base stations and their associated cells covering a given geographic area and provides interconnection to the public switched telephone network (PSTN). Each cellular exchange or cellular system is made up of one or more MSC's and its associated base stations serving the mobiles within a particular geographic area. In the United States all service areas are covered by two (2) competing carriers, called "A" and "B" carriers.
Each base station provides service to its cell through a multiplicity of both control and voice channels. The set of control channels is small relative to the voice channels and the frequencies of the control channels are known in all subscriber units via the system design. The forward control channel is used by the base station to indicate its presence, to alert subscriber units to incoming calls, and to assign voice channels for calls requested by subscriber units over the reverse control channel. Once a call has been set up, control of the call (e.g. for handoff to a different cell) is achieved through control messages imbedded in the voice channel.
When a subscriber unit is first turned on, it scans all of the known forward control channels to find the strongest available signal. If none is found, it continues scanning until the subscriber enters a service area.
The forward channel contains a system identifier field (SID) encoded with the system ID number of the serving carrier. SIDs were assigned for all areas of the United States by the FCC in the design of the cellular phone system, and denote one of a multiplicity of designated metropolitan or rural service areas that roughly correspond to city and/or county boundaries. This system ID code is periodically included in the message stream on all active forward control channels for each cell. The SID is only one of several pieces of data included in the forward channel broadcast, but it is one of key interest to the instant invention.
The relationship between SID and geographic location is known and fixed by the FCC. Since this information is broadcast at all times, it is available free to any receiver capable of tuning in, demodulating, and decoding the control channels signals, however, in practical cases, a cellular phone transceiver would be the preferred receiving device.